Lithium secondary battery

ABSTRACT

The present invention relates to a lithium secondary battery including a positive electrode including a positive active material, the positive active material including a nickel-containing lithium transition metal compound; a negative electrode including a negative active material; and an electrolyte including a non-aqueous organic solvent, a lithium salt, and an additive comprising a compound represented by Chemical Formula 1, wherein the content of Ni is 60 mol % or more based on 100 mol % of the total transition metals in the lithium transition metal compound.wherein, in Chemical Formula 1, A is a substituted or unsubstituted aliphatic chain or (—C2H4—O—C2H4—)n, and n is an integer from 1 to 10.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation-in-part of U.S. patent applicationSer. No. 16/335,240, filed on Mar. 20, 2019, which is a National PhasePatent Application of International Patent Application NumberPCT/KR2017/009934, filed on Sep. 11, 2017, which claims priority ofKorean Patent Application No. 10-2016-0126806, filed on Sep. 30, 2016.The entire contents of all of which are incorporated herein byreference.

TECHNICAL FIELD

This disclosure relates to a lithium secondary battery.

BACKGROUND ART

A portable information device such as a cell phone, a laptop, smartphone, and the like or an electric vehicle has used a lithium secondarybattery having high energy density and easy portability as a drivingpower source.

In general, a lithium secondary battery is manufactured by usingmaterials capable of reversibly intercalating and deintercalatinglithium ions as a positive active material and a negative activematerial and filling an electrolyte between the positive electrode andthe negative electrode.

Lithium-transition metal oxides are used as the positive active materialof the lithium secondary battery, various types of carbon-basedmaterials are used as the negative active material, and lithium saltsdissolved in the non-aqueous organic solvent are used as an electrolyte.

In particular, as a lithium secondary battery exhibits batterycharacteristics by complex reactions such as those between a positiveelectrode and an electrolyte, a negative electrode and an electrolyte,and the like, the use of a suitable electrolyte is one of importantparameters for improving the performance of a lithium secondary battery.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

Embodiments provide a lithium secondary battery exhibiting good storagestability, while good cycle-life characteristics are maintained.

Technical Solution

In one aspect, the present disclosure provides a lithium secondarybattery including a positive electrode including a positive activematerial, the positive active material including a nickel-containinglithium transition metal compound; a negative electrode including anegative active material; and an electrolyte including a non-aqueousorganic solvent, a lithium salt, and an additive including a compoundrepresented by Chemical Formula 1, wherein a content of nickel (Ni) isabout 60 mol % or more based on 100 mole % of the total transitionmetals (e.g., all transition metals) in the lithium transition metalcompound.

In Chemical Formula 1, A is a substituted or unsubstituted aliphaticchain or (—C₂H₄—O—C₂H₄—)n, and n is an integer from 1 to 10.

Advantageous Effects

According to the embodiments, storage stability of a lithium secondarybattery may be improved, while good cycle-life characteristics aremaintained.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a lithium secondary battery according toan embodiment of the present disclosure.

FIG. 2 shows CV characteristic evaluation results of Example 1.

FIG. 3 shows CV characteristic evaluation results of Comparative Example1.

FIG. 4A shows LSV evaluation results of Example 1 and ComparativeExample 1.

FIG. 4B is an enlarged view showing a y-axis scale of FIG. 4A.

FIG. 5 shows the results of measurement of cycle characteristics forExample 2 and Comparative Example 2.

MODE FOR INVENTION

Hereinafter, the present disclosure will be described more fullyhereinafter with reference to the accompanying drawings, in whichexemplary embodiments of the invention are shown. However, thisdisclosure may be embodied in many different forms and is not construedas limited to the example embodiments set forth herein.

In order to clearly illustrate the present invention, parts that are notrelated to the description are omitted, and the same or similarcomponents are denoted by the same reference numerals throughout thespecification.

Sizes and thicknesses of components in the drawings are arbitrarilyexpressed for convenience of description and, thus, the presentinvention is not limited by the drawings.

In addition, unless explicitly described to the contrary, the word“comprise” and variations such as “comprises” or “comprising,” will beunderstood to imply the inclusion of stated elements but not theexclusion of any other elements.

An electrolyte of a lithium secondary battery may be generally anorganic solvent in which a lithium salt is dissolved. In particular,non-aqueous organic solvents having a high ionic conductivity anddielectric constant and a low viscosity may be used.

In lithium secondary battery using a carbonate-based solvent of such anon-aqueous organic solvent, an irreversible side reaction may occurbetween the electrolyte and the positive electrode, and between theelectrolyte and the negative electrode at a high temperature and a highpressure.

The decomposition products produced by such a side reaction form a thickpassivation film which acts as a resistance on the surface of theelectrode and decrease a cycle life and capacity of the lithiumsecondary battery. Also, due to the decomposition of a carbonate-basedorganic solvent, gas is generated inside the battery which causes aswelling phenomenon and it may lead to battery explosion.

A lithium secondary battery according to one embodiment includes anelectrolyte (including a compound represented by Chemical Formula 1 asan additive). Here, the electrolyte composition for a lithium secondarybattery prevents or reduces a swelling phenomenon of a lithium secondarybattery and has excellent stability and cycle-life characteristics. Thatis, the lithium secondary battery according to one embodiment includes apositive electrode including a positive active material, the positiveactive material including a nickel-containing lithium transition metalcompound; a negative electrode including a negative active material; andan electrolyte including a non-aqueous organic solvent, a lithium salt,and an additive including a compound represented by Chemical Formula 1.

In Chemical Formula 1, A is a substituted or unsubstituted aliphaticchain or (—C₂H₄—O—C₂H₄—)n, and n is an integer from 1 to 10.

In Chemical Formula 1, A may be a C₂ to C₂₀ hydrocarbon chain or(—C₂H₄—O—C₂H₄—)n, and n may be an integer from 1 to 5.

In addition, the compound represented by Chemical Formula 1 may be acompound represented by Chemical Formula 1-1.

The nickel-containing lithium transition metal compound positive activematerial may be a high-Ni positive active material having a content ofNi of 60 mol % or more in the nickel-containing lithium transition metalcompound.

According to the one embodiment, the nickel-containing lithiumtransition metal compound positive active material may be represented byChemical Formula 4.Li_(p)(Ni_(x)Co_(y)Me_(z))O₂  [Chemical Formula 4]

wherein in Chemical Formula 4, 0.9≤p≤1.1, 0.6≤x≤0.98, 0<y≤0.3, 0<z≤0.3,x+y+z=1, and

Me is at least one of Al, Mn, Mg, Ti, and Zr.

The high-Ni positive active material has higher gas generation duringthe charge and discharge compared to a cobalt-based or a manganese-basedpositive active material, or a low-Ni positive active material having acontent of Ni of less than 60 mol %. As described above, the lithiumsecondary battery according to one embodiment includes the positiveelectrode with the high-Ni positive active material and the electrolyteincluding the compound represented by Chemical Formula 1 as an additiveso that (when the electrolyte including an additive including thecompound represented by Chemical Formula 1 is applied to a lithiumsecondary battery with the high-Ni positive active material), theeffects such as the improvement in the cycle-life characteristics of thelithium secondary battery and the decrease in the generation of gas at ahigh temperature may be further enhanced or maximized. By using (e.g.,utilizing) the electrolyte with the compound of Chemical Formula 1 asthe additive which is capable of reducing the amount of gas generation,the enhanced or maximum effects may be obtained. Furthermore, when theelectrolyte including the compound of Chemical Formula 1 as the additiveis used together with the high-Ni positive active material such as thecompound of Chemical Formula 4, resistance during the storage,particularly, storage at high temperatures, may be reduced.

As described above, the effect for decreasing the gas generation fromthe compound represented by Chemical Formula 1 is caused (e.g.,produced) by the included difluorophosphite (—OPF₂) group havingexcellent electrochemical reactivity at both terminals.

During the initial charge of a lithium secondary battery, lithium ions,which are released from the positive active material, i.e., the positiveelectrode, are transported into a carbon electrode which is a negativeelectrode and intercalated thereinto. Because of its high reactivity,lithium reacts with the carbon electrode to produce Li₂CO₃, LiO, LiOH,etc., thereby forming a thin film on the surface of the negativeelectrode. This thin film is referred to as a solid electrolyteinterface (SEI) film. The SEI thin film formed during the initial chargeprevents the reaction between lithium ions and carbon negative electrodeor other materials during charge and discharge. In addition, it alsoacts as an ion tunnel, allowing the passage of only lithium ions. Theion tunnel prevents disintegration of the structure of the carbonnegative electrode, which is caused by co-intercalation of organicsolvents of the electrolyte, having a high molecular weight along withsolvated lithium ions into the carbon negative electrode. Once the SEIthin film is formed, lithium ions do not react again with the carbonnegative electrode or other materials, such that the amount of lithiumions is reversibly maintained. Therefore, in order to improve thehigh-temperature cycle characteristics and the low-temperature output ofthe lithium secondary battery, a rigid SEI thin film must be alwaysformed on the negative electrode of the lithium secondary battery.

However, when the additive including the compound represented byChemical Formula 1 is included like (e.g., as in) the electrolyte for alithium secondary battery according to the present disclosure, a rigidSEI film having good ion conductivity is formed on the surface of thenegative electrode, and thereby it is possible to suppress adecomposition of the surface of the negative electrode during hightemperature cycle operation and to prevent an oxidation reaction of theelectrolyte solution.

When the compound represented by Chemical Formula 1 is decomposed, adifluorophosphite (—OPF₂) group and an ethylene dioxide fragment may beformed.

The difluorophosphite (—OPF₂) group may form a donor-acceptor bond withtransition metal oxide that is exposed on the surface of the positiveactive material due to excellent electrochemical reactivity and thus aprotective layer in a form of a composite may be formed.

In addition, the difluorophosphite (—OPF₂) adhered to the transitionmetal oxide at the initial charge of the lithium secondary battery maybe oxidized to a plurality of fluorophosphates, and thus more stableinactive layer having excellent ion conductivity may be formed on apositive electrode. Therefore, it is possible to prevent othercomponents of the electrolyte from being oxidation-decomposed, and as aresult, the cycle-life performance of the lithium secondary battery maybe improved and a swelling phenomenon may be prevented from occurring.

Further, the compound represented by Chemical Formula 1 and its oxideparticipate in the electrochemical reaction with the components of theSEI thin film to make the SEI thin film more rigid and to improvestability of other components included in the electrolyte by oxidativedecomposition.

In addition, the compound represented by Chemical Formula 1 forms acomposite with LiPF₆ and thus undesirable side reactions may beprevented from occurring, and it is possible to improve cycle-lifecharacteristics of the lithium secondary battery and to prevent thegeneration of gas in the lithium secondary battery, therebysignificantly reducing an occurrence rate of defects due to a swellingphenomenon.

On the other hand, the additive including the compound represented byChemical Formula 1 may be included in an amount of 0.1 wt % to 3 wt %based on a total amount of the electrolyte for a lithium secondarybattery. More specifically, the amount of the compound represented byChemical Formula 1 may be 0.5 wt % to 1.5 wt %. When the amount of theadditive satisfies the above ranges, a resistance increase may beprevented and the amount of the generated gas may be effectivelydecreased and thus a lithium secondary battery having improvedcycle-life characteristics may be realized.

The additive for a lithium secondary battery of this disclosure mayfurther include an additional additive. The additional additive may be,for example, at least one selected from the group consisting offluoroethylene carbonate, vinylethylene carbonate, vinylene carbonate,succinonitrile, hexane tricyanide, lithium tetrafluoroborate, andpropane sultone, but is not limited thereto.

Herein, an amount of the additional additive may be 0.1 wt % to 20 wt %based on a total amount of the electrolyte for a lithium secondarybattery. More specifically, the amount of the additional additive may be0.1 wt % to 15 wt %. When the amount of the additional additivesatisfies the above ranges, battery resistance may be effectivelysuppressed and a lithium secondary battery having cycle-lifecharacteristics may be realized.

On the other hand, the non-aqueous organic solvent serves as a mediumfor transporting ions taking part in the electrochemical reaction of alithium secondary battery.

The non-aqueous organic solvent may include a carbonate-based,ester-based, ether-based, ketone-based, alcohol-based, or aproticsolvent.

The carbonate-based solvent may include dimethyl carbonate (DMC),diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropylcarbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate(MEC), ethylene carbonate (EC), propylene carbonate (PC), butylenecarbonate (BC), and/or the like. The ester-based solvent may includemethyl acetate, ethyl acetate, n-propyl acetate, dimethylacetate,methylpropionate, ethyl propionate, propyl propionate, γ-butyrolactone,decanolide, valerolactone, mevalonolactone, caprolactone, and/or thelike.

The ether-based solvent may include dibutyl ether, tetraglyme, diglyme,dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and/or thelike, and the ketone-based solvent may include cyclohexanone, and/or thelike.

The alcohol-based solvent may include ethanol, isopropyl alcohol, and/orthe like, and the aprotic solvent may include nitriles such as T-CN(wherein T is a hydrocarbon group having a C2 to C20 linear, branched,or cyclic structure and may include a double bond, an aromatic ring, oran ether bond), and/or the like, dioxolanes such as 1,3-dioxolane,and/or the like, sulfolanes, and/or the like.

The non-aqueous organic solvent may be used alone or in a mixture. Whenthe organic solvent is used in a mixture, the mixture ratio may becontrolled in accordance with a desirable battery performance.

The carbonate-based solvent is prepared by mixing a cyclic carbonate anda linear carbonate. When the cyclic carbonate and linear carbonate aremixed together in a volume ratio of 1:1 to 1:9, an electrolyteperformance may be improved.

The non-aqueous organic solvent may further include an aromatichydrocarbon-based organic solvent in addition to the carbonate-basedsolvent. Herein, the carbonate-based solvent and the aromatichydrocarbon-based organic solvent may be mixed in a volume ratio of 1:1to 30:1.

The aromatic hydrocarbon-based organic solvent may be an aromatichydrocarbon-based compound of Chemical Formula 2.

In Chemical Formula 2, R₁ to R₆ are the same or different and are eachindependently selected from the group consisting of hydrogen, halogen,C1 to C10 alkyl group, haloalkyl group, and a combination thereof.

Specific examples of the aromatic hydrocarbon-based organic solvent maybe selected from benzene, fluorobenzene, 1,2-difluorobenzene,1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene,1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene,1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene,1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene,1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene,1,2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene,2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene,2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene,2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene,2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene,2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene,2,3,5-triiodotoluene, xylene, and a combination thereof.

The electrolyte of a lithium secondary battery may further include anethylene carbonate-based compound represented by Chemical Formula 3 inorder to improve cycle life of a battery.

In Chemical Formula 3, R₇ and R₈ are each independently selected fromhydrogen, a halogen, a cyano group (CN), a nitro group (NO₂), and afluorinated C1 to C5 alkyl group, provided that at least one of R₇ andR₈ is selected from a halogen, a cyano group (CN), a nitro group (NO₂),and a fluorinated C1 to C5 alkyl group, and R₇ and R₈ are notsimultaneously hydrogen.

Examples of the ethylene carbonate-based compound may be difluoroethylenecarbonate, chloroethylene carbonate, dichloroethylene carbonate,bromoethylene carbonate, dibromoethylene carbonate, nitroethylenecarbonate, cyanoethylene carbonate, fluoroethylene carbonate, and thelike. The amount of the additive for improving cycle life may be usedwithin an appropriate range.

The lithium salt dissolved in the non-aqueous solvent supplies lithiumions in a battery, enables a basic operation of a lithium secondarybattery, and improves transportation of the lithium ions betweenpositive and negative electrodes. Examples of the lithium salt includeat least one supporting salt selected from LiPF₆, LiSbF₆, LiAsF₆,LiN(SO₂C₂F₆)₂, Li(CF₃SO₂)₂N, LiN(SO₃C₂F₅)₂, LiC₄F₉SO₃, LiClO₄, LiAlO₂,LiAlCl₄, LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (wherein x and y arenatural numbers, for example, an integer from 0 to 20), LiCl, LiI,LiB(C₂O₄)₂ (lithium bis(oxalato) borate, LiBOB), LiDFOP (lithiumdifluoro bis(oxalato)phosphate), LiDFOB (lithium difluoro(oxalato)borate), and LiPO₂F₂ (lithium difluorophosphate). The lithium salt maybe used in a concentration from 0.1 M to 2.0 M. When the lithium salt isincluded at the above concentration range, an electrolyte may haveexcellent performance and lithium ion mobility due to optimalelectrolyte conductivity and viscosity.

FIG. 1 is a schematic view showing a structure of a lithium secondarybattery according to an embodiment of this disclosure.

Referring to FIG. 1, a lithium secondary battery 100 according to anembodiment may include an electrode assembly 40 and a case 50 in whichthe electrode assembly 40 is contained.

The electrode assembly 40 includes a positive electrode 10 including apositive active material, a negative electrode 20 including a negativeactive material, and a separator 30 disposed between the positiveelectrode 10 and the negative electrode 20. The positive electrode 10,the negative electrode 20, and the separator 30 may be impregnated inthe aforementioned electrolyte solution (not shown) according to thepresent disclosure.

The positive electrode 10 includes a current collector and a positiveactive material layer disposed on the current collector and including apositive active material.

In the positive active material layer, the positive active material mayinclude a compound (lithiated intercalation compound) being capable ofintercalating and deintercallating lithium and specifically at least onecomposite oxide of lithium and a metal of cobalt, manganese, nickel, anda combination thereof may be used. Specific examples thereof may be acompound represented by one of the following chemical formulae.Li_(a)A_(1-b)X_(b)D₂ (0.90≤a≤1.8, 0≤b≤0.5);Li_(a)A_(1-b)X_(b)O_(2-c)D_(c) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05);Li_(a)E_(1-b)X_(b)O_(2-C)D_(C) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05);Li_(a)E_(2-b)X_(b)O_(4-c)D_(c) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05);Li_(a)Ni_(1-b-c)Co_(b)X_(c)D_(a) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α≤2);Li_(a)Ni_(1-b-c)Co_(b)X_(c)O_(2-a)T_(a) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05,0<α<2); Li_(a)Ni_(1-b-c)Co_(b)X_(c)O_(2-α)T_(α) (0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05, 0<α<2); Li_(a)Ni_(1-b-c)Mn_(b)X_(c)D_(α) (0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05, 0<α≤2); Li_(a)Ni_(1-b-c)Mn_(b)X_(c)O_(2-α)T_(α) (0.90≤a≤1.8,0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li_(a)Ni_(1-b-c)Mn_(b)X_(c)O_(2-α)T₂(0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<a<2); Li_(a)Ni_(b)E_(c)G_(d)O₂(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1);Li_(a)Ni_(b)Co_(b)Mn_(d)G_(e)O₂ (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5,0.001≤e≤0.1); Li_(a)NiG_(b)O₂ (0.90≤a≤1.8, 0.001≤b≤0.1); Li_(a)CoG_(b)O₂(0.90≤a≤1.8, 0.001≤b≤0.1); Li_(a)Mn_(1-b)G_(b)O₂ (0.90≤a≤1.8,0.001≤b≤0.1); Li_(a)Mn₂G_(b)O₄ (0.90≤a≤1.8, 0.001≤b≤0.1);Li_(a)Mn_(1-g)G_(g)PO₄ (0.90≤a≤1.8, 0≤g≤0.5); QO₂; QS₂; LiQS₂; V₂O₅;LiV₂O₅; LiZO₂; LiNiVO₄; Li_((3-f))J₂(PO₄)₃ (0≤f≤2); Li_((3-f))Fe₂(PO₄)₃(0≤f≤2); and Li_(a)FePO₄ (0.90≤a≤1.8).

In the chemical formulae, A is selected from Ni, Co, Mn, and acombination thereof; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr,V, a rare earth element, and a combination thereof; D is selected fromO, F, S, P, and a combination thereof; E is selected from Co, Mn, and acombination thereof; T is selected from F, S, P, and a combinationthereof; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and acombination thereof; Q is selected from Ti, Mo, Mn, and a combinationthereof; Z is selected from Cr, V, Fe, Sc, Y, and a combination thereof;and J is selected from V, Cr, Mn, Co, Ni, Cu, and a combination thereof.

Particularly, in one embodiment, the positive active material ispreferably a nickel-containing lithium transition metal positive activematerial, and more preferably, a high-Ni positive active material havingthe content of Ni of 60 mol % or more (e.g., based on a total moleamount of all the transition metals in the nickel-containing lithiumtransition metal compound).

The lithium metal oxide may have a coating layer on the surface, or maybe mixed with another lithium metal oxide having a coating layer. Thecoating layer may include at least one coating element compound selectedfrom an oxide of a coating element, a hydroxide of a coating element, anoxyhydroxide of a coating element, an oxycarbonate of a coating element,and a hydroxy carbonate of a coating element. The compound for thecoating layer may be amorphous or crystalline. The coating elementincluded in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti,V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating layer may bedisposed by a method having no adverse influence on properties of apositive active material by using these elements in the compound, (e.g.,the method may include any coating method (e.g., spray coating, dipping,etc.)), but is not illustrated in more detail since it is well-known tothose skilled in the related field.

In the positive electrode, the positive active material may be includedin an amount of 90 wt % to 98 wt % based on a total weight of thepositive active material layer.

In an embodiment, the positive active material layer may include abinder and a conductive material. Herein, the binder and the conductivematerial may be included in an amount of 1 wt % to 5 wt %, respectively,based on the total amount of the positive active material layer.

The binder serves to adhere the positive active material particles withone another and to adhere the positive active material to a currentcollector and examples thereof may be polyvinyl alcohol, carboxylmethylcellulose, hydroxypropyl cellulose, diacetyl cellulose,polyvinylchloride, carboxylated polyvinylchloride, polyvinylfluoride, anethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, a styrene-butadiene rubber, an acrylatedstyrene-butadiene rubber, an epoxy resin, nylon, and the like, but arenot limited thereto.

The conductive material is included to provide conductivity to theelectrode and any electrically conductive material may be used as aconductive material unless it causes a chemical change. Examples of theconductive material may include a carbon-based material such as naturalgraphite, artificial graphite, carbon black, acetylene black, ketjenblack, carbon fiber, and the like; a metal-based material of a metalpowder or a metal fiber including copper, nickel, aluminum, silver, andthe like; a conductive polymer such as a polyphenylene derivative; or amixture thereof.

The current collector may be an aluminum foil, a nickel foil, or acombination thereof, but is not limited thereto.

The negative electrode 20 includes a current collector and a negativeactive material layer disposed on the current collector and including anegative active material.

The negative active material may include a material that reversiblyintercalates/deintercalates lithium ions, a lithium metal, a lithiummetal alloy, a material capable of doping/dedoping lithium, or atransition metal oxide.

The material that reversibly intercalates/deintercalates lithium ionsmay include for example, a carbon material, and i.e., the carbonmaterial which may be a generally-used carbon-based negative activematerial in a lithium secondary battery. Examples of the carbon-basednegative active material may include crystalline carbon, amorphouscarbon, or mixtures thereof. The crystalline carbon may be unspecifiedshaped, or sheet, flake, spherical, or fiber shaped natural graphite orartificial graphite. The amorphous carbon may be a soft carbon, a hardcarbon, a mesophase pitch carbonization product, fired coke, and/or thelike.

The lithium metal alloy includes an alloy of lithium and at least oneadditional metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si,Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

The material being capable of doping/dedoping lithium may be Si, SiO_(x)(0<x<2), a Si-Q alloy (wherein Q is an element selected from an alkalimetal, an alkaline-earth metal, a Group 13 element, a Group 14 element,a Group 15 element, a Group 16 element, a transition metal, a rare earthelement, and a combination thereof, and not Si), a Si-carbon composite,Sn, SnO₂, Sn—R (wherein R is an element selected from an alkali metal,an alkaline-earth metal, a Group 13 element, a Group 14 element, a Group15 element, a Group 16 element, a transition metal, a rare earthelement, and a combination thereof, and not Sn), a Sn-carbon composite,and the like. At least one of these materials may be mixed with SiO₂.The elements Q and R may be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti,Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os,Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As,Sb, Bi, S, Se, Te, Po, and a combination thereof.

The transition metal oxide may include lithium titanium oxide.

The negative active material layer includes a negative active materialand a binder, and optionally a conductive material.

In the negative active material layer, the negative active material maybe included in an amount of 95 wt % to 99 wt % based on the total weightof the negative active material layer. In the negative active materiallayer, a content of the binder may be 1 wt % to 5 wt % based on a totalweight of the negative active material layer. When the negative activematerial layer includes a conductive material, the negative activematerial layer includes 90 wt % to 98 wt % of the negative activematerial, 1 wt % to 5 wt % of the binder, and 1 wt % to 5 wt % of theconductive material.

The binder improves binding properties of negative active materialparticles with one another and with a current collector. The binder mayuse a non-water-soluble binder, a water-soluble binder, or a combinationthereof.

The non-water-soluble binder may be polyvinylchloride, carboxylatedpolyvinylchloride, polyvinylfluoride, an ethylene oxide-containingpolymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene,polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide,polyimide, or a combination thereof.

The water-soluble binder may be a styrene-butadiene rubber, an acrylatedstyrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, acopolymer of propylene and a C2 to C8 olefin, a copolymer of(meth)acrylic acid and (meth)acrylic acid alkyl ester, or a combinationthereof.

When the water-soluble binder is used as a negative electrode binder, acellulose-based compound may be further used to provide viscosity as athickener. The cellulose-based compound includes one or more ofcarboxymethyl cellulose, hydroxypropylmethyl cellulose, methylcellulose, or alkali metal salts thereof. The alkali metals may be Na,K, or Li. The thickener may be included in an amount of 0.1 parts byweight to 3 parts by weight based on 100 parts by weight of the negativeactive material.

The conductive material is included to provide electrode conductivityand any electrically conductive material may be used as a conductivematerial unless it causes a chemical change. Examples of the conductivematerial include a carbon-based material such as natural graphite,artificial graphite, carbon black, acetylene black, ketjen black, denkablack, a carbon fiber, and the like; a metal-based material of a metalpowder or a metal fiber including copper, nickel, aluminum silver, andthe like; a conductive polymer such as a polyphenylene derivative; or amixture thereof.

The current collector may include one selected from a copper foil, anickel foil, a stainless steel foil, a titanium foil, a nickel foam, acopper foam, a polymer substrate coated with a conductive metal, and acombination thereof.

The positive active material layer and the negative active materiallayer are formed by mixing an active material, a binder and optionally aconductive material in a solvent to prepare an active materialcomposition, and coating the active material composition on a currentcollector. The formation method of the active material layer is wellknown, and thus is not described in detail in the present disclosure.The solvent includes N-methylpyrrolidone and the like, but is notlimited thereto. When a water-soluble binder is used in the negativeactive material layer, a solvent used for preparing the negative activematerial composition may be water.

The separator 30 may include polyethylene, polypropylene, polyvinylidenefluoride, and multi-layers thereof such as a polyethylene/polypropylenedouble-layered separator, a polyethylene/polypropylene/polyethylenetriple-layered separator, or a polypropylene/polyethylene/polypropylenetriple-layered separator.

Hereinafter, the disclosure (e.g., the subject matters of thedisclosure) will be specifically examined (e.g., illustrated) throughExamples.

Example 1

(1) Positive Electrode and Negative Electrode

97.3 wt % of LiCoO₂ as a positive active material, 1.4 wt % ofpolyvinylidene fluoride as a binder, and 1.3 wt % of ketjen black as aconductive material were mixed and then, dispersed inN-methylpyrrolidone to prepare positive active material slurry. Thepositive active material slurry was coated on an aluminum foil and then,dried and compressed to manufacture a positive electrode.

98 wt % of graphite as a negative active material, 1 wt % ofpolyvinylidene fluoride as a binder, and 1 wt % of ketjen black as aconductive material were mixed and then, dispersed inN-methylpyrrolidone to prepare a negative active material layercomposition, and the negative active material layer composition wascoated on a copper foil and dried to manufacture a negative electrode.

(2) Preparation of Electrolyte

0.95 M LiPF₆ was added to a mixed solution of ethylene carbonate(EC):diethyl carbonate (DEC):ethylpropionate (EP) mixed in a volumeratio of 30:50:20 to prepare a non-aqueous mixed solution.

1.0 wt % of a compound represented by Chemical Formula 1-1 based on anamount of the non-aqueous mixed solution was added thereto tomanufacture an electrolyte for a lithium secondary battery.

(3) Manufacture of Lithium Secondary Battery Cell

The positive and negative electrodes manufactured according to the (1)and the electrolyte prepared according to the (2) were used tomanufacture a lithium secondary battery cell.

Example 2

(1) Manufacture of Positive Electrode and Negative Electrode

A positive electrode and a negative electrode were manufactured in thesame method as Example 1.

(2) Manufacture of Electrolyte

0.95 M LiPF₆ was added to a first mixed solution of ethylene carbonate(EC):ethylmethyl carbonate (EMC):ethylpropionate (EP):γ-butyrolactone(GBL) used in a volume ratio of 27:50:20:3 to prepare a second mixedsolution.

6 wt % of fluoroethylene carbonate (FEC), 0.5 wt % of vinylethylenecarbonate (VEC), 0.2 wt % of lithium tetrafluoroborate (LiBF₄), 5 wt %of succinonitrile (SN), 2 wt % of hexane tri-cyanide (HTCN), and 0.5 wt% of a compound represented by Chemical Formula 1-1 based on an amountof the second mixed solution were added thereto to prepare anelectrolyte for a lithium secondary battery.

(3) Manufacture of Lithium Secondary Battery Cell

A prismatic lithium secondary battery was manufactured by housing thepositive and negative electrodes and a polypropylene separator in acontainer and injecting the prepared electrolyte thereinto.

Example 3

A lithium secondary battery cell was manufactured according to the samemethod as Example 2 except that 0.25 wt % of the compound represented byChemical Formula 1-1 was added to prepare an electrolyte.

Example 4

A lithium secondary battery cell was manufactured according to the samemethod as Example 2 except that 1 wt % of the compound represented byChemical Formula 1-1 was added to prepare an electrolyte.

Example 5

A lithium secondary battery cell was manufactured according to the samemethod as Example 2 except that 2 wt % of the compound represented byChemical Formula 1-1 was added to prepare an electrolyte.

Comparative Example 1

(1) Manufacture of Positive Electrode and Negative Electrode

A positive electrode and a negative electrode were manufacturedaccording to the same method as Example 1.

(2) Manufacture of Electrolyte

0.95 M LiPF₆ was added to a mixed solution of ethylene carbonate(EC):diethyl carbonate (DEC):ethylpropionate (EP) used in a volume ratioof 30:50:20 to prepare a non-aqueous mixed solution.

(3) Manufacture of Lithium Secondary Battery Cell

A prismatic lithium secondary battery cell was manufactured by housingthe positive and negative electrodes manufactured in the above (1) andthe electrolyte prepared in the above (2).

Comparative Example 2

(1) Manufacture of Positive Electrode and Negative Electrode

A positive electrode and a negative electrode were manufacturedaccording to the same method as Example 1.

(2) Manufacture of Electrolyte

An electrolyte for a lithium secondary battery cell was manufacturedaccording to the same method as Example 2 except that the compoundrepresented by Chemical Formula 1-1 was not added thereto.

(3) Manufacture of Lithium Secondary Battery Cell

A lithium secondary battery cell was manufactured according to the samemethod as Example 2.

Experimental Example 1—CV Characteristics Evaluation

Cyclic voltammetry (CV) characteristics of the half-cells according toExample 1 and Comparative Example 1 were evaluated. The result ofExample 1 is shown in FIG. 2, and the result of Comparative Example 1 isshown in FIG. 3.

In FIGS. 2 and 3, 1, 3, and 5 denote the number of cycles.

Referring to FIGS. 2 and 3, currents were largely increased during bothof intercalation/deintercalation of lithium in FIG. 2 compared with FIG.3. Accordingly, when the lithium secondary battery cell including theelectrolyte using additives including the compound represented byChemical Formula 1-1 according to Example 1 was compared with thelithium secondary battery cell according to Comparative Example 1,lithium ions were relatively more easily intercalated/deintercalated.

Experimental Example 2—Evaluation of LSV Characteristics

The electrolytes of Example 1 and Comparative Example 1 were evaluatedregarding oxidation electrode decomposition at 25° C. using a linearsweep voltammetry (LSV) method. In this evaluation, a three-electrodeelectrochemical cell using a Pt electrode as a working electrode, acounter electrode, and Li as a reference electrode was used. Herein, ascan was performed in a range of 3.0 V to 7.0 V at a rate of 1 mV/sec,and the results are shown in FIGS. 4A and 4B. FIG. 4A shows LSVevaluation results of Example 1 and Comparative Example 1, and FIG. 4Bis an enlarged view showing a y-axis scale of FIG. 4A.

Referring to FIGS. 4A and 4B, the electrolyte including additivesincluding the compound represented by Chemical Formula 1-1 according toExample 1 exhibited an onset potential increase at a higher voltagecompared with the electrolyte according to Comparative Example 1.Accordingly, when the additive of Chemical Formula 1-1 was added,oxidation resistance of an electrolyte was increased.

Experimental Example 3—Thickness Increase Rate

The lithium secondary battery cells according to Example 2 andComparative Example 2 were constant current charged at current densityof 1 C until a voltage reached 4.45 V. After measuring thicknesses ofthe cells after the charge, their thickness variation ratios (%) weremeasured every seven day, while stored at 60° C. for 28 days. Thethickness variation ratios measured at the 28^(th) day were shown inTable 1.

TABLE 1 Division Thickness increase rate (%) Example 2 14.3 Example 322.9 Example 4 9.0 Example 5 11 Comparative Example 2 23.8

Referring to Table 1 and FIG. 5, the lithium secondary battery cellsusing the electrolyte including the additive of the present inventionaccording to example embodiments exhibited a significantly reducedthickness compared with the lithium secondary battery cells notincluding the additive according to Comparative Example.

Experimental Example 4—Cycle Characteristics

The lithium secondary battery cells according to Example 2 andComparative Example 2 were constant current charged at current densityof 1 C at 45° C. until a voltage reached 4.45 V. Subsequently, thelithium secondary battery cells were allowed to stand for 10 minutes andthen, discharged at constant current of 1 C, until the voltage reached 3V, and this charge and discharge as one cycle was 250 times repeated.The results are shown in FIG. 5.

Referring to FIG. 5, the lithium secondary battery cells according toExamples exhibited excellent high temperature cycle-life characteristicscompared with the lithium secondary battery cell according toComparative Example.

Example 6

(1) Positive Electrode and Negative Electrode

97.3 wt % of LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂ as a positive active material,1.4 wt % of polyvinylidene fluoride as a binder, and 1.3 wt % of ketjenblack as a conductive material were mixed and then, dispersed inN-methylpyrrolidone to prepare a positive active material slurry. Thepositive active material slurry was coated on an aluminum foil and thendried and compressed to manufacture a positive electrode.

98 wt % of graphite as a negative active material, 1 wt % ofpolyvinylidene fluoride as a binder, and 1 wt % of ketjen black as aconductive material were mixed and then dispersed in N-methylpyrrolidoneto prepare a negative active material slurry. The negative activematerial slurry was coated on a copper foil, dried and compressed tomanufacture a negative electrode.

(2) Preparation of Electrolyte

1.5 M LiPF₆ was added to a mixed solution of ethylene carbonate(EC):ethyl methyl carbonate (EMC):dimethyl carbonate (DMC) mixed in avolume ratio of 20:20:60 to prepare a non-aqueous mixed solution.

3.0 wt % of fluoroethylene carbonate and 0.5 wt % of a compoundrepresented by Chemical Formula 1-1 based on 100 wt % of the non-aqueousmixed solution were added thereto to manufacture an electrolyte for alithium secondary battery.

(3) Manufacture of Lithium Secondary Battery Cell

The positive and negative electrodes manufactured according to the (1),the electrolyte prepared according to the (2), and a polypropyleneseparator were used to manufacture a lithium secondary battery cell.

Example 7

A lithium secondary battery cell was manufactured according to the samemethod as Example 6, except that 0.75 wt % of the compound representedby Chemical Formula 1-1 was added to prepare an electrolyte.

Example 8

A lithium secondary battery cell was manufactured according to the samemethod as Example 6, except that 1.0 wt % of the compound represented byChemical Formula 1-1 was added to prepare an electrolyte.

Example 9

A lithium secondary battery cell was manufactured according to the samemethod as Example 6, except that 1.5 wt % of the compound represented byChemical Formula 1-1 was added to prepare an electrolyte.

Example 10

A lithium secondary battery cell was manufactured according to the samemethod as Example 6, except that 3.0 wt % of the compound represented byChemical Formula 1-1 was added to prepare an electrolyte.

Comparative Example 3

A lithium secondary battery cell was manufactured according to the samemethod as Example 6, except that the compound represented by ChemicalFormula 1-1 was not added to prepare an electrolyte.

Comparative Example 4

A lithium secondary battery cell was manufactured according to the samemethod as Example 6, except that 0.25 wt % of the compound representedby Chemical Formula 1-1 was added to prepare an electrolyte.

Comparative Example 5

A lithium secondary battery cell was manufactured according to the samemethod as Example 6, except that 4.0 wt % of the compound represented byChemical Formula 1-1 was added to prepare an electrolyte.

Example 11

A lithium secondary battery cell was manufactured according to the samemethod as Example 8, except that LiNi_(0.88)CO_(0.09)Mn_(0.03)O₂ wasused as a positive active material.

Example 12

A lithium secondary battery cell was manufactured according to the samemethod as Example 6, except that LiNi_(0.88)CO_(0.09)Al_(0.03)O₂ wasused as a positive active material.

Example 13

A lithium secondary battery cell was manufactured according to the samemethod as Example 7, except that LiNi_(0.88)CO_(0.09)Al_(0.03)O₂ wasused as a positive active material.

Example 14

A lithium secondary battery cell was manufactured according to the samemethod as Example 8, except that LiNi_(0.88)CO_(0.09)Al_(0.03)O₂ wasused as a positive active material.

Example 15

A lithium secondary battery cell was manufactured according to the samemethod as Example 10, except that LiNi_(0.88)CO_(0.09)Al_(0.03)O₂ wasused as a positive active material.

Comparative Example 6

A lithium secondary battery cell was manufactured according to the samemethod as Example 12, except that 0.25 wt % of the compound representedby Chemical Formula 1-1 was added to prepare an electrolyte.

Comparative Example 7

A lithium secondary battery cell was manufactured according to the samemethod as Example 12, except that 4.0 wt % of the compound representedby Chemical Formula 1-1 was added to prepare an electrolyte.

Example 16

A lithium secondary battery cell was manufactured according to the samemethod as Example 6, except that LiNi_(0.91)CO_(0.07)Al_(0.02)O₂ wasused as a positive active material.

Example 17

A lithium secondary battery cell was manufactured according to the samemethod as Example 7, except that LiNi_(0.91)CO_(0.07)Al_(0.02)O₂ wasused as a positive active material.

Example 18

A lithium secondary battery cell was manufactured according to the samemethod as Example 8, except that LiNi_(0.91)CO_(0.07)Al_(0.02)O₂ wasused as a positive active material.

Example 19

A lithium secondary battery cell was manufactured according to the samemethod as Example 10, except that LiNi_(0.91)CO_(0.07)Al_(0.02)O₂ wasused as a positive active material.

Comparative Example 8

A lithium secondary battery cell was manufactured according to the samemethod as Example 16, except that 0.25 wt % of the compound representedby Chemical Formula 1-1 was added to prepare an electrolyte.

Comparative Example 9

A lithium secondary battery cell was manufactured according to the samemethod as Example 16, except that 4.0 wt % of the compound representedby Chemical Formula 1-1 was added to prepare an electrolyte.

Comparative Example 10

(1) Manufacture of Positive Electrode and Negative Electrode

A positive electrode was manufactured according to the same method asExample 6, except that LiCoO₂ was used as a positive active material.

A negative electrode was manufactured according to the same method asExample 6.

(2) Manufacture of Electrolyte

1.5 M LiPF₆ was added to a mixed solution of ethylene carbonate(EC):ethyl methyl carbonate (EMC):dimethyl carbonate (DMC) mixed in avolume ratio of 20:20:60 to prepare a non-aqueous mixed solution.

3.0 wt % of fluoroethylene carbonate based on 100 wt % of thenon-aqueous mixed solution was added thereto to manufacture anelectrolyte for a lithium secondary battery.

(3) Manufacture of Lithium Secondary Battery Cell

The positive and negative electrodes manufactured according to the (1),the electrolyte prepared according to the (2), and a polypropyleneseparator were used to manufacture a lithium secondary battery cell.

Reference Example 1

(1) Manufacture of Positive Electrode and Negative Electrode

A positive electrode and a negative electrode were manufacturedaccording to the same method as Comparative Example 10.

(2) Preparation of Electrolyte

1.5 M LiPF₆ was added to a mixed solution of ethylene carbonate(EC):ethyl methyl carbonate (EMC):dimethyl carbonate (DMC) mixed in avolume ratio of 20:20:60 to prepare a non-aqueous mixed solution.

3.0 wt % of fluoroethylene carbonate and 1.0 wt % of a compoundrepresented by Chemical Formula 1-1 based on 100 wt % of the non-aqueousmixed solution were added thereto to manufacture an electrolyte for alithium secondary battery.

(3) Manufacture of Lithium Secondary Battery Cell

The positive and negative electrodes manufactured according to the (1),the electrolyte prepared according to the (2), and a polypropylenesearator were used to manufacture a lithium secondary battery cell.

Comparative Example 11

A lithium secondary battery cell was manufactured according to the samemethod as Comparative Example 10, except thatLiNi_(0.5)Co_(0.2)Mn_(0.3)O₂ was used as a positive active material.

Reference Example 2

A lithium secondary battery cell was manufactured according to the samemethod as Reference Example 1, except that LiNi_(0.5)Co_(0.2)Mn_(0.3)O₂was used as a positive active material.

Comparative Example 12

A lithium secondary battery cell was manufactured according to the samemethod as Comparative Example 10, except thatLiNi_(0.55)CO_(0.20)Mn_(0.25)O₂ was used as a positive active material.

Reference Example 3

A lithium secondary battery cell was manufactured according to the samemethod as Reference Example 1, except thatLiNi_(0.55)CO_(0.20)Mn_(0.25)O₂ was used as a positive active material.

Experimental Example 5—Cycle Characteristics

The lithium secondary battery cells according to Examples 6 to 19,Comparative Examples 3 to 12, and Reference Examples 1 to 3 were eachcharged and discharged at 1 C within the range of 3.0 V to 4.2 V at aroom temperature (25° C.) for 100 times. The capacity ratio of the100^(th) discharge capacity relative to the 1^(st) discharge capacitywas measured for each of the lithium secondary battery cells and theresults are shown as the cycle-life, in Table 2.

Experimental Example 6—DC-IR (Direct Current Internal Resistance)

The lithium secondary battery cells according to Examples 6 to 19,Comparative Examples 3 to 12, and Reference Examples 1 to 3 were eachstored at 60° C. for 30 days, and DC internal resistance (DC-IR) foreach of the lithium secondary battery cells was evaluated by measuring avoltage drop (V), while a current flowed at 1 C for 1 second under aSOC50 condition (charged to be 50% of charge capacity based on 100% ofthe entire battery charge capacity). The results are shown in Table 2.

Experimental Example 7—Amount of the Generated Gas

The lithium secondary battery cells according to Examples 6 to 19,Comparative Examples 3 to 12, and Reference Examples 1 to 3 were eachstored at 60° C. for 30 days, and the amount of the generated gas wasmeasured for each of the lithium secondary battery cells. The resultsare shown in Table 2.

TABLE 2 Amount of Increase rate Amount of Mol % of Ni compound of ofDC-IR generated gas in positive Chemical Cycle- after storing at afterstoring at Type of positive active Formula 1-1 life high-temperaturehigh-temperature active material material (wt %) (%) (%) (g/cc)Comparative LiCoO₂ 0 0 92 125.8 0.23 Example 10 Reference LiCoO₂ 0 1 91125.2 0.23 Example 1 Comparative LiNi_(0.5)Co_(0.2)Mn_(0.3)O₂ 50 0 91130.4 0.29 Example 11 Reference LiNi_(0.5)Co_(0.2)Mn_(0.3)O₂ 50 1 92129.9 0.28 Example 2 Comparative LiNi_(0.55)Co_(0.20)Mn_(0.25)O₂ 55 0 92126.8 0.35 Example 12 Reference LiNi_(0.55)Co_(0.20)Mn_(0.25)O₂ 55 1 92125.3 0.34 Example 3 Comparative LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂ 60 0 91130.3 0.43 Example 3 Comparative LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂ 60 0.25 91127.5 0.35 Example 4 Example 6 LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂ 60 0.5 93123.1 0.25 Example 7 LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂ 60 0.75 93 121.9 0.22Example 8 LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂ 60 1 95 120.6 0.20 Example 9LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂ 60 1.5 94 119.2 0.20 Example 10LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂ 60 3 93 121.0 0.24 ComparativeLiNi_(0.6)Co_(0.2)Mn_(0.2)O₂ 60 4 92 125.8 0.38 Example 5 Example 11LiNi_(0.88)Co_(0.09)Mn_(0.03)O₂ 88 1 93 122.2 0.28 ComparativeLiNi_(0.88)Co_(0.09)Al_(0.03)O₂ 88 0.25 92 126.8 0.37 Example 6 Example12 LiNi_(0.88)Co_(0.09)Al_(0.03)O₂ 88 0.5 93 122.9 0.31 Example 13LiNi_(0.88)Co_(0.09)Al_(0.03)O₂ 88 0.75 94 123.1 0.31 Example 14LiNi_(0.88)Co_(0.09)Al_(0.03)O₂ 88 1 94 120.9 0.27 Example 15LiNi_(0.88)Co_(0.09)Al_(0.03)O₂ 88 3 93 123.1 0.32 ComparativeLiNi_(0.88)Co_(0.09)Al_(0.03)O₂ 88 4 91 127.8 0.45 Example 7 ComparativeLiNi_(0.91)Co_(0.07)Al_(0.02)O₂ 91 0.25 92 129.1 0.40 Example 8 Example16 LiNi_(0.91)Co_(0.07)Al_(0.02)O₂ 91 0.5 93 123.7 0.32 Example 17LiNi_(0.91)Co_(0.07)Al_(0.02)O₂ 91 0.75 94 121.2 0.30 Example 18LiNi_(0.91)Co_(0.07)Al_(0.02)O₂ 91 1 94 120.7 0.26 Example 19LiNi_(0.91)Co_(0.07)Al_(0.02)O₂ 91 3 92 122.9 0.32 ComparativeLiNi_(0.91)Co_(0.07)Al_(0.02)O₂ 91 4 91 130.8 0.46 Example 9

As shown in Table 2, the lithium secondary battery cells including thepositive active material having 60 mol % or more of Ni and theelectrolyte including 0.5 wt % to 3 wt % of the additive of ChemicalFormula 1-1 according to Examples 6 to 19 exhibited low resistanceincrease rate and low amount of generated gas after storing at a hightemperature, while good cycle-life characteristics were maintainedcompared with the lithium secondary battery cells using the electrolytewith no additive, a large amount of additive, or a small amount ofadditive.

Furthermore, referring to Table 2, for the lithium secondary batterycells including the positive active material having less than 60 mol %of Ni, that is, 50 mol % and 55 mo %, according to Reference Examples 2and 3 and Comparative Examples 11 and 12, it can be shown that the useof the additive represented by Chemical Formula 1-1 (Reference Examples2 and 3) reduced the resistance increase rate and the amount of thegenerated gas after storing at a high temperate, compared to thoseincluding no additive (Comparative Examples 11 and 12), but the effectsof reduction were lower than in the Examples. From these results, theeffects obtained by using the additive of Chemical Formula 1-1 areincreased when it is used in the lithium secondary battery with thepositive active material having 60 mol % or more of Ni.

As shown in Table 2, the lithium secondary battery cells includingLiCoO₂ without Ni as the positive active material and the electrolyteincluding the additive of Chemical Formula 1-1 according to ReferenceExample 1 reduced the resistance increase rate and the amount of thegenerated gas after storing at a high temperate, compared to thatincluding LiCoO₂ as the positive active material and the electrolyteincluding no additive according to Comparative Example 10, but theeffects of reduction were lower than in the Examples.

From the above results, it can be clearly shown that the surprisinglyeffects of reduction related to the resistance increase rate and theamount of the generated gas after storing at a high temperature may beobtained by using both the positive active material having 60 mol % ormore of Ni and the electrolyte including the additive of ChemicalFormula 1-1.

While this invention has been described in connection with what ispresently considered to be practical example embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, and on the contrary, it is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims, and equivalents thereof.

DESCRIPTION OF SYMBOLS

-   -   100: secondary battery    -   10: positive electrode    -   20: negative electrode    -   30: separator    -   50: case

What is claimed is:
 1. A lithium secondary battery comprising: apositive electrode comprising a positive active material, the positiveactive material comprising a nickel (Ni)-containing lithium transitionmetal compound; a negative electrode comprising a negative activematerial; and an electrolyte comprising a non-aqueous organic solvent, alithium salt, and an additive comprising a compound represented byChemical Formula 1, wherein Ni is 60 mol % or more in content based on100 mol % of all transition metals in the lithium transition metalcompound:

and wherein, in Chemical Formula 1, A is a substituted or unsubstitutedaliphatic chain or (—C₂H₄—O—C₂H₄—)n, and n is an integer from 1 to 10.2. The lithium secondary battery of claim 1, wherein in Chemical Formula1, A is a C2 to C20 hydrocarbon chain or (—C₂H₄—O—C₂H₄—)n, and n is aninteger from 1 to
 5. 3. The lithium secondary battery of claim 1,wherein the compound represented by Chemical Formula 1 is a compoundrepresented by Chemical Formula 1-1:


4. The lithium secondary battery of claim 1, wherein thenickel-containing lithium transition metal compound is a compoundrepresented by Chemical Formula 4:Li_(p)(Ni_(x)Co_(y)Me_(z))O₂  [Chemical Formula 4] wherein in ChemicalFormula 4, 0.9≤p≤1.1, 0.6≤x≤0.98, 0<y≤0.3, 0<z≤0.3, x+y+z=1, and Me isat least one of Al, Mn, Mg, Ti, and Zr.
 5. The lithium secondary batteryof claim 1, wherein the additive is 0.1 wt % to 3 wt % in amount basedon a total amount of the electrolyte.
 6. The lithium secondary batteryof claim 5, wherein the additive is 0.5 wt % to 1.5 wt % in amount basedon the total amount of the electrolyte.
 7. The lithium secondary batteryof claim 1, wherein the additive further comprises an additionallyadditive selected from fluoroethylene carbonate, vinylethylenecarbonate, vinylene carbonate, succinonitrile, hexane tricyanide,lithium tetrafluoroborate, and propane sultone.
 8. The lithium secondarybattery of claim 7, wherein the additional additive is 0.1 wt % to 20 wt% in amount based on a total amount of the electrolyte.
 9. The lithiumsecondary battery of claim 1, wherein the nickel-containing lithiumtransition metal compound comprises Li, Ni and one or more metals otherthan Ni, and Ni is at least 60 mol % in content based on a total moleamount of Ni and the one or more metals other than Ni in the lithiumtransition metal compound.
 10. The lithium secondary battery of claim 1,wherein the lithium salt is selected from LiPF₆, LiSbF₆, LiAsF₆,LiN(SO₂C₂F₅)₂, Li(CF₃SO₂)₂N, LiN(SO₃C₂F₅)₂, LiC₄F₉SO₃, LiClO₄, LiAlO₂,LiAlCl₄, LiCl, LiI, LiB(C₂O₄)₂, LiDFOP, LiDFOB, LiPO₂F₂, andLiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂), wherein x and y are eachindependently an integer from 0 to
 20. 11. A method of manufacturing thelithium secondary battery of claim 1, the method comprising: coating apositive active material layer on a first current collector to preparethe positive electrode, the positive active material layer comprisingthe positive active material comprising the Ni-containing lithiumtransition metal compound; coating a negative active material layer on asecond current collector to prepare the negative electrode, mixing thenon-aqueous organic solvent, the lithium salt, and the additivecomprising the compound represented by Chemical Formula 1 to prepare theelectrolyte; and adding the electrolyte to the positive electrode andthe negative electrode.
 12. A lithium secondary battery additivecomprising: a compound represented by Chemical Formula 1, wherein thecompound is configured for a lithium secondary battery comprising apositive electrode comprising a positive active material, the positiveactive material comprising a nickel (Ni)-containing lithium transitionmetal compound, wherein Ni is 60 mol % or more in content based on 100mol % of all transition metal metals in the lithium transition metalcompound:

and wherein, in Chemical Formula 1, A is a substituted or unsubstitutedaliphatic chain or (—C₂H₄—O—C₂H₄—)n, and n is an integer from 1 to 10.13. A method of manufacturing the lithium secondary battery additive ofclaim 12, the method comprising: providing the compound represented byChemical Formula 1, wherein the additive is configured for the lithiumsecondary battery.